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Summer flounder growth and temperature induced mortality during the first year in southern New Jersey.
... The sudden appearance of young-of-year summer flounder at relatively large sizes (156-242 mm TL) in both weir and gill-net collections during late July and early August is puzzling. Postlarval summer flounder immigrate into the Great Bay- Little Egg Harbor estuary from November to May (Szedlmayer et al. 1992), and small numbers of pelagic and settling metamorphs have been collected in Schooner Creek throughout the winter (Able, unpublished data). Further, juveniles smaller than 100 mm were abundant in other marsh creeks sampled during June 1989 in a concurrent trawl survey in the same estuary (Szedlmayer et al. 1992). ...
... Postlarval summer flounder immigrate into the Great Bay- Little Egg Harbor estuary from November to May (Szedlmayer et al. 1992), and small numbers of pelagic and settling metamorphs have been collected in Schooner Creek throughout the winter (Able, unpublished data). Further, juveniles smaller than 100 mm were abundant in other marsh creeks sampled during June 1989 in a concurrent trawl survey in the same estuary (Szedlmayer et al. 1992). Our failure to capture age-0 summer flounder in the study creeks prior to late ronmental changes in the creeks during late July. ...
... Age and growth of summer flounder and determination of size attained during the first year of growth have been problematic (Powell 1982; Rogers and Van Den Avyle 1983; Able et al. 1990; Szedlmayer et al. 1992). Recently, Szedlmayer et al. (1992) reported that summer flounder in New Jersey reach 200-300 mm TL in their first year, with an estimated growth rate of 1.9 mm/d, based on length-frequency data. ...
Summer flounder Paralichthys dentatus were collected from intertidal and subtidal polyhaline marsh creeks in the Great Bay–Little Egg Harbor estuarine system in southern New Jersey during 1987–1990 to determine seasonality, duration of creek use by individuals, emigration rate, foraging habits, and daily growth rate of young-of-year fish in those habitats. Four hundred fifty-eight age-0 individuals (mean total length [TL], 238 mm; range, 156–312 mm) were collected from a combination of weir, seine, gill-net, and gig sampling. They were available to the collecting gear from late July through October, peaking numerically in September. Sixty-three (39%) of 162 tagged age-0 summer flounder were recaptured at least once during August–September. The average period of creek use was estimated at 17 d (range, 5–38 d) from release. Decline in percent recaptures suggested an emigration rate of 1.0%/d and 100% emigration within 50 d of release during August–October. Summer flounder appear to undergo tidal movements in and out of the creeks. Average growth rate predicted by length-frequency analysis was 1.7 mm/d, whereas growth rate measured directly from tag recaptures averaged 1.3 mm/d. Summer flounder preyed on creek fauna in order of prey abundance; Atlantic silversides Menidia menidia, mummichogs Fundulus heteroclitus, marsh grass shrimp Palaemonetes vulgaris, and sevenspine bay shrimp Crangon septemspinosa contributed most importantly to their diets. Stomach fullness of fish captured leaving the creeks on ebb tides was significantly greater than that of fish captured entering the creeks on flood tides, suggesting that summer flounder undergo tidal movements to take advantage of high concentrations of prey available in the creeks. These analyses provide compelling evidence that salt-marsh creeks in southern New Jersey are important nursery habitats for young-of-year summer flounder.
Laboratory experiments were conducted on juvenile summer flounder Paralichthys dentatus (41 to 80 mm total length) to determine low temperature tolerance (2 to 3 "C) a t 10, 20, and 30 %salinity, and to measure feeding rate, assimilation efficiency, growth rate and growth efficiency at 2, 6, 10. 14, 18 "C and 10, 20 and 30 '7' salinity. There was 100 % sunival at temperatures above 3 'C, suggesting that juvenile summer flounder are able to survive most winter water temperatures encoun-tered in north/central Mid-Atlantic Bight (MAB) estuaries. Mortality was 42 % after 16 d at 2 to 3 'C, and was highest in fish < 50 mm TL (1 g). Mean specific growth rates were not significantly different between 2 and 10 "C (mean = 0.14 % d-'), and these rates were not significantly different from zero. Mean growth rate increased to 2.4 "0 d-' at 14 ' C and 3.8 O/ O d-' at 18 OC. Ad libitum feeding rate showed a similar relationship to temperature. Mean assimilation efficiency (60.1 %) was not affected by temperature. Mean growth efficiency (K ,) was significantly lower at 6 "C (-23.1 "h) than a t 14 and 18 "C (18.4 and 22.1 %, respectively), and was highly variable. Salinity had no significant effect on any parameters measured, suggesting that factors other than salinity are controlling spatial distributions. Mortality resulting from acute exposure to low temperature probably occurs during one 2 to 4 wk period each winter Recruitment success from north/central MAB estuaries may be lower in years with late winter cold periods (i.e. March vs December) due to increased numbers of fish being exposed to lethal low temperatures. Additional mortahty probably results from low growth rates caused by sub-optimal temperatures (i.e. < 10 "C) throughout the spring. The annual contribution of new recruits from northern estuanes appears to b e dependent on winter temperature regime, particularly on the magnitude and timing of temperature minima.
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